How do I make a shadow catcher?

I want to place some text in a scene, put a light behind it and have it cast a shadow on the ground in a video, where I'll place a plane at the same angle as the ground so it looks correct.

I can do this with a light and casting the shadow onto the plane OK, but I want just the shadow, so it'll look like it's on the video's ground and not the plane itself. Various blend modes for the plane don't work and a Set Matte using the plane as a source seems overkill, so I'm stumped.

Probably something simple I'm missing, anyone care to point out what that is?

I'd gone through all the blend modes when I was using a grey plane and evidently didn't try them all again when I'd changed it to white later. Doh!

Got it working with the shadow in another comp (on white) and using a Set Matte on that with Lightness and then a Fill Color to make it darker, then duplicated it because: still not dark enough, then added some Blur.

Edit: Oops, I also need a extra light for the front of the text or it turns black, whereas the separate shadow method doesn't need a light because I just get the shadow shape from the shadow comp. An extra light is easy enough, but it might be six of one, half a dozen of the other for Hitfilm's workload on the two methods.

The Illumination settings for those are independent to the Layer Materials. As you've noted, for a 2D layer this is the Illumination dropdown. If you ever use these effects on a 3D layer like parallax on a model, which does work..., turn off Illumination in the Layer materials or the 3D layer gets lit twice.